函数返回类型中的{}有何作用？函数声明中有无{}结果为何一致？

Great questions! Let's break these down clearly:

问题1：函数返回类型中的{}有什么用途？ #

Most often, you'll see {} in a return type position in typed languages like TypeScript. Here's what it does:

• It represents an empty object type, meaning the function returns an object with no custom own properties. Note that the returned object can still have inherited properties (like toString() or valueOf() from the Object prototype)—the type just enforces no self-defined properties.
• Example in TypeScript:

  function getEmptyContainer(): {} {
    return {}; // Perfectly matches the return type
    // return { id: 123 };  Also valid, since the type allows extra properties
  }
  

• A common confusion point: In JavaScript arrow functions, if you want to return an object literal directly, you need to wrap {} in parentheses (e.g., const getUser = () => ({ name: "Zoe" })). Without the parentheses, () => { name: "Zoe" } gets parsed as a function body (where name: "Zoe" is a label statement), and the function returns undefined instead of the object.

问题2：在函数声明中，{}的作用是什么？为何调用该方法时，有无{}的执行结果完全相同？ #

Let's unpack this:

• The {} in a function declaration (or expression/arrow function) is the function body—it wraps all the code that runs when the function is called. This is where you put logic, variable declarations, and return statements.
• The "same result with or without {}" scenario almost always refers to arrow function shorthand:
  1. Shorthand (no {}): const multiply = (x, y) => x * y
  2. Full syntax (with {}): const multiply = (x, y) => { return x * y }
     These behave the same because arrow functions omit the {} to use implicit return: the expression after the arrow is automatically returned. When you add {}, you have to explicitly write return to send back the value—if you match the expression correctly, the result will be identical.
• A gotcha: If you use {} but forget the return, the function will return undefined by default. For example, const doNothing = () => {} returns undefined, same as const doNothing = () => undefined—but this is a coincidence, not intentional shorthand.
• Important note: Regular function declarations can't omit {} at all. Writing function add(a, b) a + b will throw a syntax error—this shorthand is only for arrow functions.

内容的提问来源于stack exchange，提问作者Octavian R.